The present invention relates to a system for suppressing noise due to exhaust gas issued from an engine of an automotive vehicle, and more particularly to such a system which includes a silencer whereby exhaust resistance is varied to enhance noise suppressing performance or engine output performance depending on operating conditions of the automotive vehicle.
JP No. 62-126217 discloses a noise suppressing system of the above kind. In this known noise suppressing system, a silencer is employed which exhibits noise suppressing performance variable in response to revolution speed of an engine of an automotive vehicle and load on the engine. More particularly, exhaust resistance provided by the silencer is varied by a selector valve such that the selector valve is closed to set a relatively great exhaust resistance for increased noise suppressing effect when the automotive vehicle passes through city area where the engine operates with a relatively light load, whereas the selector valve is opened to decrease exhaust resistance for increased engine output performance when the vehicle travels at high speeds or at acceleration where the engine operates with a heavy load.
However, this conventional known noise suppressing system is not effective enough to suppress internal sound created within the vehicle cabin due to exhaust sound.
An object of the present invention is to improve a system for suppressing noise due to exhaust gas issued from an engine of an automotive vehicle such that internal sound created within the vehicle cabin due to exhaust sound is considerably suppressed while keeping its noise suppressing performance and engine output performance demanded depending on operating conditions of the vehicle at sufficiently high levels.